The communication pathway between two endpoint nodes or devices sometimes traverses networks that operate according to different protocol suites. For example, most modern video terminals are designed for connection with networks that utilize the well-known H.323 standard which specifies the components, protocols, and procedures that provide multimedia communication services—audio, video, and data communications—over packet networks, including Internet Protocol (IP)-based networks. But in certain cases the communication pathway between the IP endpoints may include a connection over an Integrated Services Digital Network (ISDN), which is an international communications standard for sending voice, video, and data over digital telephone lines. Video conferencing calls made over an ISDN normally utilize the H.320 protocol suite of recommendations, which is based on aggregated communication channels (e.g., so-called Bearer or “B” channels) with data throughput rates that are integer multiples of 64,000 bits per second (64 Kbps). A gateway device is typically used to inter-connect the two dissimilar networks.
When H.320 is used to inter-connect two IP video endpoints—e.g., a H.323, Session Initiation Protocol (SIP), or Skinny Client Control Protocol (SCCP) compatible endpoint device—multiple ISDN calls may be required to provide adequate bandwidth. In such cases, a primary call is placed to provide an in-band control message path via a H.221 along with bandwidth for audio and video payload. A number of secondary calls (e.g., B channels) are then established to provide additional bandwidth for the video and data payload. H.221 is part of the H.320 recommendations and defines a frame structure for audiovisual calls over single or multiple 64 Kbps channels; that is, how frames of audio, video, data, and control information are multiplexed and synchronized onto an ISDN channel. The problem with network architectures such as these, however, is that the call setup time may be exceedingly long depending on the establishment and synchronization of the H.221 FAS (Frame Alignment Signal) and BAS (Bit-rate Allocation Signal) channel. Also, it may take noticeable time for the video terminals to start displaying video once a call connection has been established, depending on when all the bearer channels synchronize to each other.